Radiotherapy treatment monitoring using ultrasound

ABSTRACT

Methods and systems for assessing the effects of therapy on a patient include obtaining baseline and treatment ultrasound scans of a treatment area of a patient where the treatment ultrasound scans are taken subsequent to the baseline scan and at various times during a course of radiotherapy treatment sessions. The baseline and treatment ultrasounds are compared, and as a result a damage map representing cell death within the treatment area can be constructed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationSer. No. 60/611,361, filed Sep. 20, 2004, the entire disclosure of whichis hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to methods and systems for monitoring therapytreatments, and more specifically to observe cell degradation overmultiple radiotherapy treatment fractions.

BACKGROUND INFORMATION

In radiotherapy, radiation dosages are typically defined in terms of theenergy absorbed per unit mass of tissue. However, relating theprescribed physical dose to the biological effect the radiation willhave on the actual tissue being treated is not straightforward. FIG. 1,for example, illustrates these potential dose-response curves 100indicating the surviving fraction of cells during a treatment protocolversus the administered dose. The dose-response curves can vary amongpatients, and even at various locations or times for a particularpatient. The actual dose-response curve for a particular patient and/ororgan, however, is typically not well known in-vivo.

Typically, radiotherapy treatment for deep-seated tumors (as well as tosome superficial organs such as the skin) is delivered in a number offixed sessions, or fractions (e.g., one fraction a day for 30 days) andthe dosages are prescribed primarily based on physician and/orinstitutional experience. For a given total dose, the dose-responsecurve of a fractional scheme is affected, for example, by the effect ofDNA repair and biological damage due to ionizing radiation (or by othertherapies such as cryotherapy and chemotherapy). In particular,radiation can directly or indirectly cause breaks in DNA strands, whichunder some circumstances may be repaired, but in other cases may not be,resulting in cell death.

More particularly, two primary types of cell death occur as a result ofradiation exposure—mitotic cell death and apoptosis. In mitotic celldeath (which may occur at any time following irradiation), damagedchromosomes cause cells to die as they attempt to divide. Apoptosis, orprogrammed cell death, occurs normally, and although not typically asprominent as mitotic cell death, can also be induced by radiation andcorrelate with radiosensitivity.

Because cell death occurs at different rates for different patients,cells, tissues, organs and tumors, dose-response curves for anyindividual treatment can vary significantly. Therefore, it is difficultto determine, a priori, the proper dose that will kill a given patient'stumor without exposing healthy tissue to unacceptable levels ofradiation. Further, the effects of each treatment fraction (bothimmediately following the fraction and prior to a subsequent fraction)can impact the dose-response curve for a particular treatment. What isneeded, therefore, is a way to determine the amount (or lack of) damagecaused by therapy dosages, thus giving the physician the ability todetermine appropriate adjustments to the therapeutic dosages throughoutthe treatment cycle that account for the effects of previous radiationfractions on an individual patient's anatomy.

SUMMARY OF THE INVENTION

The invention utilizes ultrasonic tissue characterization techniques asan in-vivo monitoring and/or prediction system of biological damage dueto ionizing radiation over the course of a series of radiotherapyfractions, and for follow-up monitoring of the radiation effects. Inthis way it is possible to determine the effectiveness of a radiotherapytreatment as well as other types of cancer therapy to assist physicians,technicians and radiobiologists in determining if treatmentmodifications are warranted, as well as a way to document and understandthe relationship between dosages and in-vivo damage to cancerous cellsand surrounding healthy tissue.

In accordance with the present invention, a series of low-frequencyultrasound (<20 MHz) scans are used to determine a cell survivalfraction (or a surrogate quantity therefor) in-vivo, for tumorsundergoing radiotherapy. The invention goes beyond measuring physicaldoses using point dosimeters and exit dosimetry, and unlikehigh-frequency measurement of apoptosis, measures cell survival overtime in three-dimensions—i.e. before, during and after treatment forvarious sections of the treatment area. Furthermore, by using lowerfrequencies, the invention can determine changes to cellular size,structure, and/or survival in deep-seated tissues and tumors as well asthose closer to the surface. These changes can be viewed over anextended period of time and may be extrapolated into the future, thusassessing the effectiveness of the treatment as (and after) it isdelivered (or proposed to be delivered) to the patient.

In one aspect, the present invention provides a method for assessing theeffects of treatment on cell condition including the steps of obtaininga baseline ultrasound scan of a treatment area of a patient, andobtaining subsequent, temporally distinct ultrasound scans of thetreatment area at various times. The subsequent (“treatment”) scans aretaken during the course of (or, in some cases, sometime after) varioustreatment sessions, and the baseline scan and the subsequent scans arecompared. The method further includes constructing a damage map(depicting, for example, the spatial distribution and/or progression ofcell death) of the treatment area based on the comparison.

In some embodiments, the baseline scans and/or treatment scans can betwo- or three-dimensional ultrasound scans. The ultrasound scans can betaken using a low-frequency ultrasound scanner at a frequency below 20MHz, for example. The treatment sessions can be one or more of radiationtreatment, chemotherapy, cryotherapy, and/or brachytherapy. In somecases, the ultrasound treatment scans can be taken following and/orpreceding a treatment session. A B-mode scan can be taken prior to thebaseline scan (or any of the treatment scans) to determine an anatomicalfeature of interest within (or near) the treatment area. In someembodiments, the feature may be segmented in the B-mode scan.

Construction of the damage map may include characterizing the powerspectrum from the baseline scan, the treatment scans, or both. In someembodiments a damage map constructed from one of the treatment scans canbe superimposed with a damage map constructed from the baseline scan (orsubsequent treatment scans). A series of damage maps can be constructedusing the baseline scan and the treatment scans, and used to build apredictive model that predicts the effects of future radiotherapysessions on tissue, and to plan subsequent radiotherapy treatmentsessions. As one example, the method can include selecting ahypothetical radiation dosage and delivery pattern and, using thepredictive model, generate an expected tissue damage map resulting fromthe dosage and delivery pattern. The comparisons among the baseline scanand the treatment scans can also be used to determine an average damagevalue for a region.

In another aspect, a system for determining cell condition in responseto treatment includes a register for receiving baseline and treatmentultrasound scans of a treatment area, where the treatment ultrasoundscans are taken subsequent to the baseline scan and at various timesduring a course of treatment sessions. The system also includes acomparator module for comparing the baseline ultrasound scan and thetreatment ultrasound scans and, based on the comparison, constructing adamage map representing cell death within the treatment area.

In some embodiments, the system includes a display (either static orinteractive) for displaying the damage map, and may also include one ormore input devices to allow users to adjust treatment parameters, enterdata, and/or manipulate the ultrasound scans.

In another aspect, the invention provides software in computer-readableform for performing the methods described herein.

BRIEF DESCRIPTION OF FIGURES

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention.

FIG. 1 is a graphical representation of various dose-response curvesillustrating the surviving fraction of cells versus radiation dose fordifferent treatments.

FIG. 2 is a schematic diagram illustrating the use of a hand-heldimaging device to obtain data used to construct an initial map of alesion in accordance with one embodiment of the invention.

FIG. 3 is a schematic diagram illustrating the delivery of radiotherapyto the lesion of FIG. 2.

FIG. 4 is a schematic diagram illustrating the use of a hand-heldimaging device to obtain data to construct a treatment map of a lesionduring the course of radiotherapy in accordance with one embodiment ofthe invention.

FIG. 5 is a graphical representation of the average biological damage ina region of interest before, during and after being subjected to one ormore radiation treatments.

FIG. 6 is a graphical representation of the power spectrum calculatedfrom data acquired in accordance with one embodiment of the invention.

FIGS. 7A-7D are schematic illustrations of tissue health within atreatment area in accordance with one embodiment of the invention.

FIG. 8 is a schematic illustration of a biological damage monitoringsystem according to an embodiment of the invention.

DETAILED DESCRIPTION

Throughout the following descriptions and examples, the invention isdescribed in the context of monitoring and measuring the effects ofradiotherapy as administered to a cancerous tumor or lesion. However, itis to be understood that the present invention may be applied tomonitoring various physical and/or biological attributes of virtuallyany mass within or on a patient in response to any form of treatment.For example, the therapy can include one or more of radiation,cryotherapy, or any other treatment method that can affect tissuebiology at the cellular level.

Typically, B-mode medical ultrasound consists of pressure waves(referred to as RF image data) that are detected by transducers andconverted to pixel values by extracting the envelope of the waves. Oneimaging parameter in ultrasound is the operational frequency. Generally,the higher the frequency, the better the intrinsic resolution of theimages produced by the ultrasound system. Because the attenuation ofultrasonic waves increases as the frequency is increased, higherfrequencies (e.g., 10 MHz) are typically chosen for imaging ofsuperficial structures, and lower frequencies (e.g., 3 MHz) are used forimaging deep-seated structures. In addition, high-frequency ultrasoundimaging uses frequencies above 20 MHz to observe the effects of varioustreatments at the cellular level.

Referring to FIG. 2, a series of low-frequency (<20 MHz) ultrasonic RFdata scans are acquired at various times before, during and after thecourse of a patient's radiotherapy treatment, which is typically givenin many fractions over an extended period of time. For example, an RFultrasound scan is taken of a deep-seated tumor 205 within theillustrated region of a patient P prior to administration of the firstradiotherapy fraction. The scan can be taken in one, two, or threedimensions to obtain ultrasonic RF data, using, for example, a hand-heldultrasonic scanning device 210. This initial scan 215 is deemed to bethe “baseline”—i.e., the planning or preparation scan. At various timesthroughout the course of radiotherapy treatment, the patient isrescanned in a similar fashion. The subsequent scanning can be done justfollowing the administration of a new radiotherapy fraction, just priorto a fraction, at any point (or points) between fractions, and/or afterthe last fraction.

In addition to being useful for visualization of a patient's anatomy,there is additional information in the RF image data which can becompared to RF image data from prior scans and/or the baseline,facilitating identification of biological changes among any set of scans(including the baseline scan). These changes can then be used todetermine a one-, two-, or three-dimensional map of biological celldamage due to the effects of radiotherapy. Thus, the various ultrasoundscans taken over time, when viewed together, act as an in-vivobiological dosimeter, indicating the effective dosage that was deliveredto a particular treatment area of the patient (as well as to tissuesoutside the treatment region) and the resulting tissue damage.

In some embodiments, B-mode ultrasound scans are obtained prior to theinitial baseline ultrasound scan to identify the relevant anatomicalregions of interest, thus aiding the guidance of the subsequentultrasound. Further, the B-mode scans may be used to enhance the visualdisplay of the damage map by overlaying the B-mode scan with the damagemap image. The B-mode scan can also be used to facilitate thecalculation of various treatment parameters (e.g., average of tissuedamage over a given tumor site or organ), and to account for the effectof organ motion and shape changes.

Referring to FIG. 3, sometime after the baseline scan is obtained, thefirst radiotherapy treatment is administered to the tumor 205 using, forexample, an external single-beam conformal radiation device 300 that canbe rotated around the patient to administer treatment from variousangles. In other embodiments, a multi-beam device may be used. As shownin FIG. 4, immediately following the treatment (or some short timethereafter), a post-radiation ultrasound scan (a “treatment scan”) 405is acquired. Data from the treatment scan 405 provides an indication ofthe state of both the remaining tumor cells 205, the dead cells 410killed by the radiotherapy, as well as one or more anatomical features,such as an organ 420 as imaged using the B-mode scan referenced above.By analyzing the various post-irradiation and baseline RF scanparameters, a biological damage map can be constructed, which in turnmay be used by the physician to determine the effectiveness of thetreatment (and the extent of unwanted damage to healthy tissue)throughout the region of interest (or at particular points of interest)and possibly to alter the treatment plan accordingly.

Because cell death is not necessarily manifested immediately after atreatment session (it may take hours, days or even months), the variousRF scans can be obtained at any time before, during and after the courseof treatment, such as prior to and/or after each treatment session. Inaddition to a full map of biological damage, an average measure ofbiological damage over a region of interest, such as a segmentedstructure or lesion, can also be calculated and plotted over timethroughout and after treatment, thereby providing the physician anindication of treatment efficacy for specific regions within thetreatment area.

Referring to FIG. 5, for example, tumor 205 is depicted as it appears inthe baseline scan, with a high degree of cell survival prior to theadministration of the first radiotherapy treatment. A series oftreatment fractions 505 (Tx₁ through Tx_(m)) is delivered, and at one ormore times between the fractions the treatment ultrasounds are obtainedshowing non-uniform, non-linear tissue damage over time, with portionsof the tumor remaining untreated, and other portions 405 having beenirradiated. In other cases, portions of the tumor may have receivedtreatment, but due to one or more factors (e.g., radioresistancy) thetreatment may not have been effective to kill the cancerous cells. Thisdata can be plotted throughout treatment to ensure the radiotherapy iskilling the intended cells. In some instances, a scan 510 can beobtained subsequent to the last fraction to determine the full effectsof the treatment, which may not be apparent for weeks, or even monthsafter treatment.

As a result, the RF image data from ultrasound scans taken with eachsuccessive treatment can be used to construct a model describing theextent to which tissue damage is accumulating (or not accumulating), andin some cases, at what regions within the treatment area (or along whichdirections) it is accumulating more than others. The model provides botha spatial and time-based view of how the radiotherapy is affecting thatparticular patient's cells at various locations within the treatmentarea due to the cumulative effects of the dosages over time, and thevariations in tissue densities and sensitivities at various locationswithin the treatment area. The model may then be used to generate apredicted map of tissue response to the next proposed treatment orseries of treatments, thus allowing a physician to alter the treatmentplan if the predicted tissue response is not consistent with thetreatment goals, or somehow varies from the theoretical response assumedduring the treatment planning stage. Further, a physician may specifydifferent doses and exposure areas for subsequent treatments, and, usingthe model, obtain a predicted tissue damage map for each hypotheticaltreatment, using the results to select the most appropriate treatmentparameters.

More specifically, one way of determining a damage map from the RF scansincludes characterizing the power spectrum for the regions of interestsurrounding each pixel or voxel representing the ultrasound scan. Forexample and with reference to FIG. 6, the RF image data expressed as asignal amplitude over space is transformed (using, e.g., a Fouriertransform) into a power spectrum 605 showing the signal's power as afunction of frequency. Other techniques for calculating the powerspectrum, such as the maximum entropy method, may also be used. Thepower spectrum may be calculated over a larger region, such as theentire treatment volume, a portion of the treatment volume, or an organor a lesion of interest in order to obtain a “regional” damage value. Insome cases, the damage map can be calculated for particular pixel orvoxel by calculating the power spectrum for an area including the pixelor voxel of interest and those adjacent to it. In some embodiments, aknown reference material (e.g., glass) is used to obtain a calibratedpower spectrum, and the subsequent spectra may then be normalized usingthe calibrated spectrum.

To relate the power spectrum 605 to tissue damage and/or health, variousanalytical parameters such as the intercept 610, slope and midband fit615 of the power spectrum can be extracted from the RF image data, andthese parameters in turn can be used to derive the acousticconcentration of scatterers, CQ², where C is the concentration ofscatterers (an indication of the surviving fraction of cells) and Q isthe relative impedance of the scatterers. (See, for example, Lizzi F.L., Astor M., Liu T., Deng C., Coleman D. J., Silverman R. H.,“Ultrasonic Spectrum Analysis for Tissue Assays and Therapy Evaluation”Int. J. Imaging Syst. Technol. 8, 3-10, 1997). In some cases, C can beisolated and used as a direct representation of cell survival and tissuehealth, but, in cases where C cannot be isolated and where Q² remainsrelatively constant over time for a particular frequency, CQ² can beused as a surrogate for C, and thus as an adequate representation oftissue health. The difference in C and/or CQ² (or related quantities)over time and/or at different points within or around the treatment areagives an indication of the surviving fraction of cells during the courseof radiotherapy at various points in space. These differences can, insome embodiments, be built up from smaller regions within and/or aroundthe treatment area to produce a tissue damage map of the entiretreatment area, thus relating treatment dosages to variations in tissuehealth in two- or three-dimensions for a particular anatomical area of aparticular patient, at a particular time. A model relating tissue damageto dosage and time is obtained from the individual, time-specific damagemaps using conventional curve-fitting or interpolation techniques. Usingthis model, physicians can then predict the effect of a particular dose(or series of doses) at a particular time for a specific anatomical areaof an individual patient.

Analysis of the RF image data can involve such analytical quantities asthe power spectrum, autocorrelation function (i.e., the correlation ofthe RF signal with itself), and attenuation estimates, but can also orinstead include other quantities. These quantities represent variousways of detecting relative changes in tissue makeup from RF image data,and can either be averaged in a region of interest or displayed in full.Alternatively or in addition, parameters such as the slope of the powerspectrum can be extracted from these quantities. Instead of or inaddition to a region-of-interest average, the spatial variation of theseparameters can be displayed and analyzed in three dimensions. As onegoal of the invention is to describe changes in the parameters over thecourse of treatment to determine tissue damage, a difference, ratio, orother mathematical operation between sets of images and/or sets ofparameters can also be calculated, and the results may change thephysician's treatment decisions regarding length of treatment ortreatment modality. In some cases, the quantities may be followed overthe entire course of treatment, whereas in other embodiments, over somefraction of the treatment regimen.

FIGS. 7A-7D illustrate one possible way the damage map described abovemay be used to adjust treatment parameters in response to non-uniform orunforeseen cell damage during the course of a series of radiotherapytreatment fractions. An initial baseline image (FIG. 7A) illustrates twogroupings of cells, cancerous cells 705 (shaded) and healthy cells 710(unshaded). Using the baseline image as a guide, the physiciandetermines a treatment course, using the theoretical tissue damageprogression (FIG. 7B). The theoretical damage progression may includeone or more assumptions regarding absorption, density, sensitivity etc.and therefore indicates that the radiotherapy will kill off cellsstarting in the upper left, and move diagonally downward and to theright across the map, resulting in dead cells 715, to-be-treatedcancerous cells 705, and the remaining healthy cells 710. Using thetechniques described above, however, the resulting damage map (FIG. 7C)obtained from a treatment ultrasound image indicates quite a differentresult. Instead of progressing as intended, the radiotherapy hasaffected previously healthy cells 720 and had no effect on cancerouscells 725. Noting this deviation from the theoretical damage map (FIG.7B), the physician can adjust various treatment parameters such as beamangles, dosages and patient position mid-treatment. As a result, thepost-adjustment damage map (FIG. 7D) indicates that the previouslyunaffected cancerous cells 730 are now killed off, and cell damage hasnot progressed at the boundary 735 of healthy cells and dead cells. Asmentioned above, this two-dimensional modeling can be extended to threedimensions using three-dimensional ultrasound imaging techniques.

In some instances, determination of tissue-specific properties fromultrasound RF image data can be affected by transducer-dependenteffects, which are generally not desirable. One way to compensate forthese effects is to utilize a “phantom” to calibrate the imaging deviceand normalizing data received during normal usage to data acquired usingthe phantom. Alternatively, data can be normalized to either thebaseline scan or an earlier scan of the particular patient, thuscreating a patient-specific calibration, which in some cases may be moreaccurate than a phantom-based calibration.

One variation of the invention includes acquiring one or morethree-dimensional freehand B-mode ultrasound scans prior to the RF datascans (or each such scan, if desired) and segmenting (i.e., partitioninginto discrete volumes) the anatomy of interest at each treatment stagefrom the B-mode scan. Such an approach provides anatomical guidance forthe subsequent RF scans, and also facilitates the analysis of the RFdata in anatomical regions of interest that may change shape andposition over time. For example, the B-mode images of a prostate glandbeing treated for cancer can be segmented both before and aftertreatment delivery, and RF data analysis parameters can subsequently beaveraged within each prostate volume. Alternatively, the map ofbiological damage can be superimposed on the B-mode anatomical scan forvisualization.

The technique is not only applicable to radiation therapy but to anyother therapy which leads to tissue damage, e.g., the immediate oreventual killing of cells. Such therapies can include, for example,chemotherapy, cryotherapy, single-fraction radiosurgery, hyperthermia,or brachytherapy, or any combination of these treatment methods.Comparison of the set of scans to the baseline scan provides a directmeasurement of the effectiveness of the treatment in both time andspace, allowing the physician to adapt the treatment based on theresults.

Referring to FIG. 8, one embodiment of a system 800 for performing thetechniques described above includes a register 805 or other volatile ornon-volatile storage device that receives image data from an imagingdevice 810 (such as a hand-held ultrasound device) via a cord or wire,or in some embodiments via wireless communications. The system alsoincludes a comparator module 815 that, based on the image data, uses thetechniques described above to construct a damage map of the treatmentarea. In some embodiments, the system also includes a display 830 and anassociated user interface (not shown) allowing a user to view andmanipulate the ultrasound images and/or damage maps. The display 830 anduser interface can be provided as one integral unit or separate units(as shown) and may also include one or more user input devices 840 suchas a keyboard and/or mouse. The display 830 can be passive (e.g., a“dumb” CRT or LCD screen) or in some cases interactive, facilitatingdirect user interaction with the images and models through touch-screens(using, for example, the physician's finger as an input device) and/orvarious other input devices such as a stylus, light pen, or pointer. Thedisplay 830 and input devices 840 may be located in a different locationthat the register 805 and/or comparator 815, thus allowing users toreceive, view, and manipulate images in remote locations using, forexample, wireless devices, handheld personal data assistants, notebookcomputers, among others.

In various embodiments the register 805 and/or comparator module 815 maybe provided as either software, hardware, or some combination thereof.For example, the system may be implemented on one or more server-classcomputers, such as a PC having a CPU board containing one or moreprocessors such as the Pentium or Celeron family of processorsmanufactured by Intel Corporation of Santa Clara, Calif., the 680x0 andPOWER PC family of processors manufactured by Motorola Corporation ofSchaumburg, Ill., and/or the ATHLON line of processors manufactured byAdvanced Micro Devices, Inc., of Sunnyvale, Calif. The processor mayalso include a main memory unit for storing programs and/or datarelating to the methods described above. The memory may include randomaccess memory (RAM), read only memory (ROM), and/or FLASH memoryresiding on commonly available hardware such as one or more applicationspecific integrated circuits (ASIC), field programmable gate arrays(FPGA), electrically erasable programmable read-only memories (EEPROM),programmable read-only memories (PROM), programmable logic devices(PLD), or read-only memory devices (ROM). In some embodiments, theprograms may be provided using external RAM and/or ROM such as opticaldisks, magnetic disks, as well as other commonly storage devices.

For embodiments in which the invention is provided as a softwareprogram, the program may be written in any one of a number of high levellanguages such as FORTRAN, PASCAL, JAVA, C, C++, C^(#), LISP, PERL,BASIC or any suitable programming language. Additionally, the softwarecan be implemented in an assembly language and/or machine languagedirected to the microprocessor resident on a target device.

It will therefore be seen that the foregoing represents an improvedmethod and supporting system for monitoring the biological effects ofradiotherapy over the course of a treatment regimen. The terms andexpressions employed herein are used as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.Moreover, although the above-listed text and drawings contain titlesheadings, it is to be understood that these title and headings do not,and are not intended to limit the present invention, but rather, theyserve merely as titles and headings of convenience.

1. A method of assessing cell condition in response to treatment, the method comprising the steps of: a. obtaining a baseline ultrasound scan of a treatment area of a patient; b. obtaining, subsequent to the baseline scan, one or more temporally distinct treatment ultrasound scans of the treatment area at various times during a course of treatment sessions; c. comparing at least one of the one or more treatment ultrasound scans to the baseline ultrasound scan; and d. based on the comparison, constructing a damage map representing cell damage within the treatment area.
 2. The method of claim 1 wherein the baseline ultrasound scan is rendered in two dimensions.
 3. The method of claim 1 wherein the one or more treatment ultrasound scans are rendered in two dimensions.
 4. The method of claim 1 wherein the baseline ultrasound scan is rendered in three dimensions.
 5. The method of claim 1 wherein the one or more treatment ultrasound scans are rendered in three dimensions.
 6. The method of claim 1 wherein the baseline ultrasound scan is taken at a frequency below 20 MHz.
 7. The method of claim 1 wherein the one or more of treatment ultrasound scans are taken at a frequency below 20 MHz.
 8. The method of claim 1 wherein the treatment sessions include one or more session of radiation treatment, chemotherapy, cryotherapy, and brachytherapy.
 9. The method of claim 1 wherein each of the one or more treatment ultrasound scans are obtained substantially just following one of the treatment sessions.
 10. The method of claim 1 wherein each of the one or more treatment ultrasound scans are obtained substantially just prior to one of the treatment sessions.
 11. The method of claim 1 further comprising obtaining, prior to obtaining the baseline ultrasound scan, a B-mode scan to determine an anatomical feature of interest within the treatment area.
 12. The method of claim 11 further comprising creating a segmented representation of the anatomical feature of interest using the B-mode scan.
 13. The method of claim 1 further comprising obtaining, prior to obtaining the one or more treatment ultrasound scans, a B-mode scan to determine an anatomical feature of interest within the treatment area.
 14. The method of claim 1 wherein constructing the damage map comprises characterizing the power spectrum from one or more of the baseline scan and treatment scans.
 15. The method of claim 14 wherein the power spectrum is characterized by estimating the acoustic concentration of scatters in one or more of the baseline scan and treatment scans.
 16. The method of claim 1 further comprising constructing a series of damage maps using none or more of the baseline scan and the treatment ultrasound scans.
 17. The method of claim 16 wherein the series of damage maps provide a predictive model of tissue damage due to the treatment.
 18. The method of claim 17 further comprising the steps of: a. selecting a hypothetical radiation dosage and delivery pattern; and b. using the predictive model, generating an expected tissue damage map resulting from the hypothetical radiation dosage and delivery pattern.
 19. The method of claim 1 further comprising using the results of the comparison to plan a subsequent treatment session.
 20. The method of claim 1 further comprising using the results of the comparison to determine an average damage value depicting an average measure of cell damage over a region of interest.
 21. The method of claim 1 further comprising superimposing the damage map with a damage map constructed from the baseline ultrasound scan.
 22. A system for determining cell condition in response to treatment, the system comprising: a storage unit for receiving ultrasound scans of a treatment area, the ultrasound scans comprising: a baseline ultrasound scan; and one or more temporally distinct treatment ultrasound scans of the treatment area taken subsequent to the baseline scan and at various times during a course of treatment sessions; and a comparator module for comparing the baseline ultrasound scan and at least one of the one or more treatment ultrasound scans and, based on the comparison, constructing a damage map representing cell condition within the treatment area.
 23. The system of claim 22 further comprising a display for displaying the damage map.
 24. The system of claim 22 further comprising an ultrasound scanning device for obtaining the baseline ultrasound scan and the one or more temporally distinct treatment ultrasound scans.
 25. The system of claim 22 further comprising an input device for facilitating one or more of manipulating the ultrasound images, adjusting treatment parameters, and entering analysis data.
 26. The system of claim 25 further comprising an analysis module for predicting, in response to the damage map and the one or more treatment parameters, effects of subsequent radiotherapy treatments on the treatment area.
 27. An article of manufacture having computer-readable program portions embodied thereon for determining cell condition in response to treatment, the article comprising computer-readable instructions for: a. obtaining a plurality of temporally distinct ultrasound scans of a treatment area at various times during a course of treatment sessions; c. comparing the plurality of ultrasound scans; and d. constructing a damage map representing cell condition within the treatment area based on the comparison.
 28. The article of manufacture of claim 27 further comprising computer-readable instructions for characterizing a power spectrum from one or more of the plurality of ultrasound scans.
 29. The article of manufacture of claim 27 further comprising computer-readable instructions for constructing a series of damage maps using the baseline scan and at the one or more treatment ultrasound scans.
 30. The article of manufacture of claim 29 further comprising computer-readable instructions for constructing a predictive model of tissue damage due to treatment based on the series of damage maps.
 31. The article of manufacture of claim 30 further including computer-readable instructions for: a. selecting a hypothetical radiation dosage and delivery pattern; and b. using the predictive model, generating an expected tissue damage map resulting from the hypothetical radiation dosage and delivery pattern.
 32. The article of manufacture of claim 27 further including computer-readable instructions for superimposing the damage map with a damage map constructed from the baseline ultrasound scan. 